Purpose :
There is a lack of established animal models for glaucoma filtration surgery due to rapid postoperative subconjunctival scarring, which hinders surgical success. This scarring may be modulated using antifibrotics such as Mitomycin C (MMC). We investigated the rabbit as a potential model for glaucoma filtration after an ab interno gel stent implantation (XEN 45, Allergan plc) with and without intraoperative MMC.

Methods :
Adult New Zealand White rabbits (n=5 each group) were unilaterally implanted with the stent with or without subconjunctival MMC (10 µg) injection at the implant site. IOP measurements and ocular examinations were performed to evaluate safety and effectiveness of the stent. Bleb morphology and stent placement was evaluated by optical coherence tomography (OCT) imaging. Indocyanine green (ICG; 10 µl of 2.5 µg/µL) dye was injected intracamerally to visualize aqueous outflow post-surgery.

Results :
Significant IOP reduction of 27.5±7% in MMC group and 20.8±6% in non-MMC group was observed one day post-surgery. In non-MMC group, IOP returned to baseline level within 2 weeks postoperatively (Wk2). In contrast, MMC group showed an average of 30.5±1.7% IOP reduction up to Wk16, with peak reduction of 38.9±4.3% at Wk4; at Wk20, only 14.6±5.5% IOP reduction was observed. In both groups, visible blebs were apparent immediately post-surgery. In non MMC group, blebs flattened out by Wk2, and OCT imaging showed presence of scar tissue enveloping the stent at Wk4. In MMC group, blebs remained visible at Wk20 in eyes with reduced IOP. OCT imaging revealed presence of clear fluid-filled spaces and loosely organized subconjunctival tissue in functioning blebs. ICG imaging showed aqueous outflow via the stent towards the bleb from the anterior chamber. The stent was well-tolerated in rabbits with no significant bleb-related complications.

Conclusions :
This rabbit model is well-suited when exploring minimally invasive glaucoma surgical procedures. XEN45 gel stent surgery in conjunction with a single intraoperative MMC dose is effective in achieving sustained long-term IOP reduction and bleb survival in rabbits, although the blebs in this model differ in morphology from that observed in humans. Accelerated scarring observed in the absence of intraoperative MMC provides the opportunity to investigate novel antifibrotics in vivo.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.